Computer-assisted surgery (CAS) is a generally known and practically used surgery method, wherein a surgical operation is planned and/or conducted using a 3D model of a body section to be treated. In particular, the 3D model can be used for planning the steps of a surgical operation, e.g. the motion and adjustment of surgical tools or implants, for monitoring the surgical operation, or for constructing a real 3D implant. Typically, the 3D model can be generated on the basis of image data collected with medical imaging of a patient, e.g. by an image registration of Computed Tomography (CT) data or magnetic resonance imaging (MRI) data of the body section with CT or MR data of a certain portion of the body section.
If image data of a complete body section are not available, e.g. due to a defect such as destruction after an accident or a disease, or due to a congenital defect, generating model data for a 3D model requires a completion of the collected real image data with reconstructed data. As an example, CAS applications in Cranio-Maxillar-Facial surgery (CMF surgery) may require a reconstructed patient 3D model for obtaining complete skull image data.
Most animals are bilaterally symmetric, including humans. Animals that are bilaterally symmetric have a mirror symmetry in the sagittal plane, which divides the body vertically into left and right halves, with one of each sense organ and limb pair on either side. This is also referred to as plane symmetry. Furthermore, also individual body sections, organs, etc. may have a mirror symmetry, meaning that they could be divided into matching halves by drawing a line or plane down the center, so that the right half is a mirror image of the left half.
With one-sided defects of a body section with mirror symmetry, completion of collected data can be obtained by mirroring of the healthy half to the pathological half (see C. Mertens et al., Image data based reconstruction of the midface using a patient-specific implant in combination with a vascularized osteomyocutaneous scapular flap, Journal of Cranio-Maxillo-Facial Surgery (2012), http://dx.doi.org/10.1016/j.jcms.2012.09.003). With two-sided defects, mirroring of the healthy portions to the pathological portions is also possible if an anatomical region is not affected by corresponding defect portions on both sides of the mirror plane.
According to a proposed solution in the prior art, the mirror plane is positioned and drawn manually in the imaging data during preoperative planning by an expert, e.g. a surgeon. This process is a very time-consuming preoperative planning step because the result must be checked several times and the plane of symmetry must be repeatedly adjusted. As a further disadvantage, when performed manually, this 3D positioning of the plane of symmetry is prone to failures since the quality of the resulting 3D model essentially depends on the experience of the surgeon.